I believe if you are changing numbers within the range you defined in the pivot table, you can just right click and refresh.
If you are actually adding rows or colums of data, then the pivot table will be blind to them until you change the range settings (via Pivot Table wizard). Also, you'll need to go into the layout and let the pivot table know that you want to add the new data to its display.
Basically, I think you're right, it's nearly as easy to just make the whole pivot table over again.
If you're adding columns and you don't have any data for the rows, you could always put a column title and leave the rest of that column blank. Then select the area including that column for the pivot table but choose not to display its data until you've got data entered for it.
Also, if you insert rows/columns inside of the range you've already defined, you can use refresh to get the new data. For instance, if you've chosen A1:D10 for your range and you want to start a new column, instead of adding it at E, insert a column somewhere between A and D, then the pivot range will expand and when you hit refresh, you'll se the new column has been included.